Crate fermat_core 

fermat-core

128-bit fixed-point decimal arithmetic for Solana’s sBPF runtime.

Design Goals

• no_std: Works on Solana sBPF without any OS dependencies.
• Zero external dependencies: Only proptest appears as a dev-dependency.
• Panic-free: Every fallible operation returns Result<_, ArithmeticError>.
• #![forbid(unsafe_code)]: No unsafe blocks anywhere in the crate.
• Overflow-safe mul_div: Uses a 256-bit intermediate (U256) to prevent the class of bugs where (a × b) / c silently wraps when a × b overflows i128.

Core Type

Decimal { mantissa: i128, scale: u8 }
value = mantissa × 10^(-scale)

The scale is bounded to [0, 28] (MAX_SCALE). On-chain Borsh encoding is exactly 17 bytes (16 bytes mantissa LE + 1 byte scale).

Quick Start

use fermat_core::{Decimal, RoundingMode};

let price  = Decimal::new(150_000_000, 6).unwrap(); // 150.000000
let amount = Decimal::new(2_500_000,   6).unwrap(); //   2.500000
let total  = price.checked_mul(amount).unwrap();    // 375.000000...
let result = total.round(6, RoundingMode::HalfEven).unwrap();

Re-exports

pub use decimal::Decimal;

pub use decimal::MAX_SCALE;

pub use decimal::SOL_SCALE;

pub use decimal::USDC_SCALE;

pub use error::ArithmeticError;

pub use rounding::RoundingMode;

Modules

arithmetic

Arithmetic operations: add, sub, mul, div, mul_div, neg, abs.

compare

Ord and PartialOrd for Decimal with automatic scale normalisation.

convert

Conversions between Decimal and primitive types.

decimal

Core Decimal type definition and constants.

display

Display and Debug formatting for Decimal.

error

Error types for fermat-core arithmetic operations.

rounding

IEEE 754-2008 rounding modes and the Decimal::round method.